The present invention relates to a silicon-on-insulator ("SOI") substrate and method of fabricating the same, and more particularly to a SOI substrate and method of fabricating the same including a Si device layer having a constant thickness.
In general, in a fabrication process of a complementary metal oxide semiconductor ("CMOS") transistor, an isolation region of a large area should is needed in order to isolate devices and prevent latch-up of a CMOS transistor. There are, however, problems in that an isolation region of a large area results in a reduced chip dimension and a reduced integration of devices.
A SOI technique had been proposed in order to above problems. With complete isolation between devices, a SOI substrate, having a buried oxide film sandwiched between a Si handling substrate and a Si device substrate, prevents latch-up of a CMOS transistor and allows for high operational speed of devices.
One fabrication method of the SOI substrate is a separation by implanted oxygen ("SIMOX") method. In a conventional SIMOX technique, referring to FIG. 1A, there is a Si substrate 1 doped with impurity ions. Oxygen ions are implanted into the substrate 1. Referring to FIG. 1B, an annealing is carried out to form a buried oxide film 2 and a Si device layer 1A in the Si substrate 1. Referring to FIG. 1C, a field oxide 3 is formed in the Si device layer 1A by a LOCOS, thereby forming a SOI substrate 100.
However, the conventional SIMOX technique has a disadvantage in that dislocation in a surface of a Si layer easily occurs when implanting oxygen ions, thereby generating a great quantity of leakage current. Therefore, it is difficult to control a thickness of the Si layer where a device is to be formed.
Another method of fabrication is a bonding technique. In conventional bonding technique, referring to FIG.2A, there are provided a Si device substrate 10 and a handling substrate 11. A buried oxide film 12 is formed on the handling substrate 11 by a thermal oxidation. Referring to FIG. 2B, the handling substrate 11 and the device substrate 10 are bonded, with the buried oxide film 12 existing between substrates 10 and 11. Afterwards, most of the device substrate 10 is etched by grinding and lapping and then the ground and lapped device substrate 10 is chemical and mechanical polished to high degree of precision, thereby forming a Si device layer 10A. Referring to FIG. 2C, an isolation film 13 is formed in the Si device layer 10A to define an active region, thereby forming a SOI substrate 200 having a Si device layer 10A.
According to the conventional bonding technique, it is difficult to precisely control a polishing stop point in chemical and mechanical polishing to form the Si device layer 10A. Since, the thickness of the Si device layer 10A is not constant, yield of semi-conductor devices is reduced. In addition, the conventional bonding technique has disadvantages of a complicated fabrication process and high fabrication cost. Furthermore, the conventional techniques have a shortcoming in that a separate additional process, which forms a field oxide in a Si device layer, is required in order to define an active region.